Solid oxide fuel cells (SOFCs) operate by converting chemical energy directly to electricity by way of an isothermal electrochemical oxidation process that is not governed by the Carnot cycle thermodynamics characteristic of other energy conversion devices. SOFCs typically possess efficiencies approaching 90 percent and therefore require lower energy input to produce a specific amount of power. Additionally, SOFC performance is relatively independent of the power plant size.
During operation of a SOFC, an oxidant such as air or some other oxygen-containing medium typically is introduced at a cathodic portion of the fuel cell, and a fuel such as hydrogen, carbon monoxide, natural gas, or coal-derived gas is introduced at an anodic portion. Upon application of an external load, oxygen at the cathode (air electrode) reacts with incoming electrons from an external circuit to generate oxygen ions, which then migrate to the anode (fuel electrode) through an oxygen ion-conducting electrolyte within the body of the fuel cell. At the anode, the fuel is electrochemically oxidized with these oxygen ions to liberate electrons to an external circuit. The oxidation occurring at the fuel electrode causes current to flow through the external circuit, returning electrons to the air electrode to form more oxygen ions.
Traditionally, solid oxide fuel cells have been fabricated as multiple-component assemblages such as laminates which during operation suffer from a variety of problems attributable to thermal, mechanical, and chemical incompatibilities between each component. These problems have included poor fuel tolerance, limited chemical and thermal endurance, complex and expensive fabrication techniques, and poor mechanic durability. For example, many multiple-component fuel cells can only be energized and de-energized a few times before the component layers de-laminate due to differential thermal expansion and contraction.
Accordingly, there exists a need for new fuel cells which eliminate or at least minimize the problems associated with multiple component structures.